A power supply controller includes a switch element for permitting/inhibiting power supply from a power source to a load in order to control power supply to the load by turning the switch element on and off. In such a power supply controller, if an overcurrent flows, the switch element may burn out or a wire (power supply path) may smoke in some cases. Accordingly, a configuration is necessary in which if the overcurrent flows, the switch element would be held in the off-state to inhibit currents from flowing to the load, thereby protecting the switch element and the wire.
Generally, a semiconductor switch and a wire are different from each other in terms of thermal characteristics (heat generation characteristics and heat dissipation characteristics), hence power supply inhibition conditions may be different from each other. Typically, the switch element has smaller turn-on resistance and thermal capacity as compared to those of the wire. Therefore, it is necessary to immediately prohibit power supply if the value of an overcurrent is relatively large in order to protect the switch element but not necessary to do so if the value is relatively small. However, the wire has a large thermal capacity as compared to the switch element. Therefore, in order to protect the wire it is necessary to inhibit the power supply when an overcurrent flows for a long period of time even if its value is relatively small since there is a possibility of smoking. Accordingly, such differences in the power supply inhibition conditions lead to a necessity of different configurations to protect the switch element and to protect the wire respectively.
Regarding this point, conventionally a power supply controller which has a switch element protection circuit (Patent Document 1) is available. The switch element protection circuit performs a retry operation to turnoff the switch element if an overcurrent is detected and remove it from the off-state after a predetermined time (shut-off time) elapses and, if the number of times of the retry operation reaches a predetermined value, inhibits the power supply operation (retry operation). Further, the switch element protection circuit is configured to reset the number of times of performing the retry operation to zero if a state where no overcurrent is detected continues for a predetermined time (clear time) before the number of times of performing the retry operation reaches the predetermined value.    Patent Document 1: Japanese Unexamined Patent Publication No. 2007-174490